Conventionally, transmission/reception of signals for remote engine start, signals for keyless entry, and signals for passive functions between a portable device and a vehicle has been widely known. The remote engine start here is a function of starting or stopping the engine of a vehicle at a relatively remote location by operation of a portable device by a user. Also, the keyless entry is a function of performing control such as locking or unlocking of a door or the like (an opening/closing body) of a vehicle at a relatively close location by operation of a portable device by a user. Furthermore, the passive functions refer to a function of locking or unlocking a door when a user operates a door handle, a door knob switch or the like without operating a portable device, and a function of starting/stopping the engine when a user operates a push start switch or the like inside a vehicle without operating a portable device.
For example, JP 2010-220084 A discloses a transmission radio wave modulation method switching system having its aim to improve the reliability of communication establishment when a communication terminal and its communication counterpart perform wireless communication. According to this transmission radio wave modulation method switching system, as a communication method between a vehicle and an electronic key, FM modulation that is more immune to noise is selected in a case of a smart operation, a wireless locking/unlocking operation and the like, and AM modulation that reaches farther is selected in a case of a remote engine start operation and the like. Also, when an operation button for AM output is operated by long press, the modulation method is forcibly switched from the AM modulation used until then to the FM modulation, and wireless communication is performed.
Also, US 2004/0174246 A1 discloses a door opening system for a vehicle including a portable device that transmits a plurality of wireless frequencies, and a similarly coded wireless receiver. The decoding cycle of the receiver is varied depending on the channel, the frequency range, and the format of signals, but is a cycle of 2.5 seconds when using frequencies from 900 to 902.3 MHz for signals of multiple wireless frequencies. Reception of a first valid signal with respect to transmission of signals from the portable device is taken as the start, and reception is continued during the cycle time. All the signals received during the cycle are interpreted as one transmission.
Furthermore, JP 2009-278597 A discloses a multi-channel communication system whose electric power consumption required for wireless communication is reduced and wireless communication is carried out in a short time. This multi-channel communication system includes an electronic key capable of transmitting radio waves through a plurality of channels, and an in-vehicle communication control device capable of receiving radio waves transmitted from the electronic key by performing a polling operation at a predetermined cycle. After successively transmitting a plurality of first channel frames through a first channel, the electronic key successively transmits a plurality of second channel frames through a second channel of a frequency different from that of the first channel so as to carry out wireless communication even under a noise environment where reception of the radio wave of the first channel is interrupted. A dummy of a time length is added to the data contained in each second channel frame to extend the frame length of the second channel frame.
Furthermore, JP 2013-032648 A discloses a wireless communication system having its aim to keep, with respect to a smart system, the radio wave intensity of a request signal from an in-vehicle system to a portable device within a desired range, and also, to expand the coverage area of the request signal without deteriorating the noise tolerance. In this wireless communication system, a spread data signal is generated by performing spread modulation on predetermined LF data by a spread spectrum method that spreads a data signal into a wide frequency range by multiplication with a spread code, and the spread data signal is converted and amplified to a modulation signal in the LF wave band, and a request signal is transmitted to the portable device using the LF wave band.
In the case of transmitting a command signal to an in-vehicle ECU (Electronic Control Unit) from a portable device provided with the remote engine start function, the keyless entry, and the passive function, operations from a location far away from the vehicle (for example, several hundreds of meters to one kilometer) is prohibited with respect to the keyless entry and the passive function from the standpoint of security, and unlocking of the door is allowed only from a short distance away (several meters to several tens of meters). Accordingly, the portable device transmits the command signal with low transmission intensity that would reach a more or less short distance.
In contrast, with respect to the remote engine start function, the engine of a vehicle is, from the standpoint of convenience of the user, allowed to be started or stopped from a location far away from the vehicle. In this case, the command signal is transmitted at high transmission intensity that would reach the vehicle from a faraway position.
Regarding wireless communication by radio wave between a portable device and a vehicle, the radio wave frequency, intensity, transmission time and the like that are allowed are different depending on the regulations of each country or region. For example, in Japan and the U.S., a frequency of 900 MHz may be used for communication with respect to communication between a portable device and an in-vehicle ECU.
Under the regulations in both Japan and the U.S., regarding low transmission intensity such as that used by the keyless entry or the passive function, the portable device may perform signal transmission at a predetermined frequency using time enough to transmit one piece of transmission data contained in a command signal.
However, in the case of performing transmission at high transmission intensity such as that used by the remote engine start function, the regulations are different between Japan and the U.S. In Japan, the command signal has to be transmitted only after confirming that there is no radio wave at the same frequency in the surroundings. Then, if there is no radio wave at the same frequency in the surroundings, a signal with high transmission intensity may be transmitted with time enough to just transmit all of one piece of transmission data contained in a command signal for the remote engine start function.
On the other hand, in the U.S., there is no need to check the presence/absence of a radio wave at the same frequency in the surroundings. However, the time when transmission is possible is determined according to the transmission intensity, and in the case of transmitting at high transmission intensity such as that used by the remote engine start function, the time when transmission is possible is extremely short compared to Japan. Thus, it is not possible to transmit all of one piece of transmission data contained in the command signal for the remote engine start function.
Also, in the case of the remote engine start function, no inconvenience is caused to the user even if the response time (the time between complete start or stop of the engine to reception by the portable device of a notice regarding the completion) is a little slow. On the other hand, in the case of the keyless entry function or the passive function, if the response time is slow and the door locking/unlocking operation is delayed, a user may be dissatisfied.